For those of Ghillie's pets that require Dex to be spent to keep the pet in play, this Dex is spent at the start of Ghillie's turn. Note that pets all have their own turns and these turns happen before Ghillie's turn, so even if you choose not to spend a Dex to keep them in play, they will still get a turn ahead of Ghillie's turn before being removed from the battle.